t - Structural Fire Engineering Research at the University of Sheffield

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+. −. =∆. 1. 3. 1. 1. /. /. 10/. ,. EN 1993-1-2 calculation of protected steel temperature. EN 13481-4 calculation of fire protection material thermal conductivity ...
Intumescent Coating Performance under Different Fire Conditions Yong Wang & Jifeng Yuan, University of Manchester

1

Background 

 





Performance based fire engineering design is more widely taken up Intumescent coating 50% market share Intumescent coating performance is fire dependent Assessment of intumescent coating based on standard fire tests sufficient? If not, what is the alternative?

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Current Assessment Method: BS 13481-4 EN 1993-1-2 calculation of protected steel temperature

∆Ts =

(T (d

f

− Ts )Ap / V

 1  ) λ ρ / C p p ,t a a 1 + φ   3 

(

)

∆t − eφ / 10 − 1 ∆θt

EN 13481-4 calculation of fire protection material thermal conductivity

  V 1 φ /10 λ p ,t (t ) =  d p × × ca ρ a × (1 + φ / 3) ×  ×  ∆Ts + (e − 1)∆θt  Ap (T f − Ts )∆t  

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Fire Tests  

Under standard fire exposure Under two types of parametric fire curves

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Standard Fire Tests

5

Parametric Fire Tests 1200

Slow Fire Fast Fire

Fire Temperature (C )

1000

800

600

400

200

0 0

15

30

45

60

75

90

Time (min)

6

Basis of Parametric Fires  



Room is 5 x 5 m2, and 3m high. Normal weight concrete wall with thermal conductivity λ=1.6W/mK, density ρ=2300kg/m3, and specific heat C=980J/kgK. Window size: 1.68m wide and 1.2m high

Number of Windows

Corresponding Opening factor (m-1/2)

Fire load (kg [wood]/ m2 floor area)

Test 1

1

0.02

30

Test 2

4

0.08

100

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Test set-up Sample 1: 254mmX254mm Sample 2

Sample 1

Flange 25.3mm Web

15.6mm

DFT 0.569mm in fast fire 0.615mm in slow fire Sample 2: 203mmX203mm Flange 12.5mm Web

8.0mm

DFT 0.839mm in fast fire 0.834mm in slow fire

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After the Tests Slow fire test

Fast fire test

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Thermal Conductivity

Effective Thermal Conductivity 0.5 0.45 0.4 0.35 0.3 0.25 0.2 0.15 0.1 0.05 0 0

200

400

600

800

Temperature

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Confirmation of Back Analysis 1000 900 Temperature (C)

800 700 600 500 400 300 200 100 0 0

1000

2000

3000

4000

Time (s)

11

Prediction of Parametric Fire Tests: using effective thermal conductivity (green) and new method (black) Temperature (C)

254 Flange 800 700 600 500 400 300 200 100 0 0

1000

2000

3000

4000

5000

6000

Time (s)

Slow Fire 12

Prediction Results continued Temperature(C)

254 Web 800 700 600 500 400 300 200 100 0 0

1000

2000

3000

4000

5000

6000

Time(s)

Slow Fire

13

Prediction Results continued Temperature(C)

203 Flange 800 700 600 500 400 300 200 100 0 0

1000

2000

3000

4000

5000

6000

Time(s)

Slow Fire

14

Prediction Results continued Temperature(C)

203 Web 800 700 600 500 400 300 200 100 0 0

1000

2000

3000

4000

5000

6000

Time(s)

Slow Fire

15

Prediction Results continued 254 Flange

Temperature(C)

1200 1000 800 600 400 200 0 0

1000

2000

3000

4000

5000

6000

Time (s)

Fast Fire

16

Prediction Results continued Temperature (C)

254 Web 1200 1000 800 600 400 200 0 0

1000

2000

3000

4000

5000

6000

Time (s)

Fast Fire

17

Prediction Results continued Temperature (C)

203 Flange 1200 1000 800 600 400 200 0 0

1000

2000

3000

4000

5000

6000

Time (s)

Fast Fire

18

Prediction Results continued Temperature (C)

203 Web 1200 1000 800 600 400 200 0 0

1000

2000

3000

4000

5000

6000

Time (s)

Fast Fire

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Summary 



It is not appropriate to extrapolate effective thermal conductivity values obtained under the standard fire condition to parametric fire conditions New method provides much better results

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Basis of New Method 

Define chemical reactions and associated mass loss Reaction rate constant (Arrhenius Equation): K j = Aj exp( −

∂m j

Mass loss rate:

∂t

= m j K j f (α ) α :

Ej ℜT

), j = 1, 2,3

Degree of conversion

Key Chemicals :1. :1. Inorganic acid sources, 2. Blowing agent 3. Charring material 

Determine expansion process Expansion rate: ∂x

∂t 

=

1 ∂m2 ρ g ∂t

( x ≤ Emax x0 )

Emax: Final expansion ratio

Thermal conductivity of porous material with changing porosity Coating = Solid phase + Gas phase (Gas phase conductivity 8 λ rad = deσ T 3 Radiation part: λ = λ d: Bubble size 3 +λ g

 

cond

)

rad

Heat of decomposition, required in the chemical reaction Convection heat loss from gas transport

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Hypothesis The aforementioned parameters are intrinsic properties of an intumescent coating. Therefore, they are applicable to different fire conditions. These properties can be determined by independent means that are not fire dependent.

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Kinetic Values by Thermogravimetric Analysis (TGA) 120 100 80

Mass 60 40

fraction 20 0 0

200

400

600

800

1000

A1

300

A2

2000000

A3

5

E1

54000

E2

110000

E3

60000

Y1

28

Y2

17

Y3

55

Vc

0.65

Temperature

23

Bubble Size: Slow Fire

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Bubble Size: Fast Fire

25

Expansion Coefficients   -

Slow Fire Large section: Web=44, Flange=36 Small section: Web=50, Flange=39 Fast Fire Large section: Web=44, Flange=31 Small section: Web=48, Flange=44

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Method to Determine Expansion    

Temperature to start expansion Temperature to complete expansion Time between these two temperatures Expansion factor related to time duration Emax

Tc T2 T1

t1

t2

Time

t2-t1

27

Summary - 1    



Current method of assessment not applicable to different fire conditions The proposed method provides a feasible alternative Main material input data: chemical kinetics, bubble size, maximum expansion rate Kinetics constants to be obtained from TGA. They can be assumed to be constants for an intumescent coating product. Bubble size can be measured from small scale tests. It can be assumed to be a constant for an intumescent coating product.

28

Summary - 2 





Expansion rate requires further study. A method has been outlined. A new EPSRC funded project will start in the new year to find a method to determine expansion rate and to perform comprehensive validation of the new method for different products and different fire conditions. Future: different intumescent coating products for different “realistic (parametric)” fires?

29

Acknowledgements

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